1. Industrial Field of the Invention
The present invention relates to an electro-optical device including an electro-optical material such as a liquid crystal disposed between electrodes, and particularly to a semiconductor device (hereinafter also referred to as an IC) used in an electro-optical device to drive an electro-optical material. More particularly, the present invention relates to a configuration of pixels in an active matrix electro-optical panel having an electro-optical material such as a liquid crystal disposed between a pair of substrates.
2. Description of the Related Art
There are various types of electro-optical devices designed to drive an electro-optical material between electrodes. One such device is a simple-matrix liquid crystal device which uses a liquid crystal as the electro-optical material and which includes, as shown in FIG. 9, a first substrate 1 made of transparent and alkali-free glass or the like and a second substrate 2 also made of transparent and alkali-free glass or the like wherein transparent electrodes are formed on the opposing surfaces of the respective substrates. Upon one of the substrates, there is disposed a sealing member 3 formed of a photo-setting resin or a thermosetting resin containing spacer elements by means of a printing technique or the like. The first substrate 1 and the second substrate 2 are adhesively bonded to each other via the sealing member 3 such that they are spaced a predetermined distance apart from each other. A liquid crystal is disposed and sealed in a sealing region 4 which is partitioned, by the sealing member 2, within the gap between the first substrate 1 and the second substrate 2.
In this liquid crystal device, the first substrate 1 is greater in size than the second substrate 2, and thus the first substrate 1, on which the second substrate 2 is disposed, extends outward from the lower surface of the second substrate 2 beyond an edge of the second substrate 2. On the extending part of the first substrate 1, an IC mounting area 9 is formed adjacent to the sealing region 4, and a driving IC 14 is disposed in the IC mounting area 9 by means of a COG (chip on glass) technique. In an area adjacent to the IC mounting area 9 on the extending part, a plurality of input terminals 12 are formed along an edge of the first substrate 1, and a flexible board 29 is connected to these input terminals 12.
FIGS. 10 and 11 are plan views illustrating the layout patterns of transparent electrodes formed on the first substrate 1 and the second substrate 2, respectively, of the liquid crystal device shown in FIG. 9.
Referring to FIG. 10, an electrode pattern 70 formed on the inner surface of the first substrate 1 includes a plurality of stripe-shaped electrodes (first electrodes) 7a extending in a vertical direction within the sealing region 4 partitioned by the sealing member 3 (in an area denoted by an alternate long and short dash line L), and also includes wiring lines 7b formed outside the sealing region 4 so as to electrically connect the stripe-shaped electrodes 7a to the IC mounting area 9. The electrode pattern 70 is made of an ITO (indium tin oxide) film or the like.
In FIG. 11, an electrode pattern 60 formed on the inner surface of the second substrate 2 includes a plurality of stripe-shaped electrodes (second electrodes) 6a extending in a horizontal direction within the sealing region 4 partitioned by the sealing member 3 (in the area denoted by the alternate long and short dash line L), and also includes wirings 6b formed outside the sealing region 4 so as to electrically connect the stripe-shaped electrodes 6a to the respective terminals. The electrode pattern 60 is also made of an ITO (indium tin oxide) film or the like.
The first substrate 1 and the second substrate 2 constructed in the above-described manner are adhesively bonded to each other such that the stripe-shaped electrodes 7a of the first substrate 1 and the stripe-shaped electrodes 6a of the second substrate 2 cross one another thereby forming a plurality of pixels at respective intersections in the form of a matrix. An alignment film (not shown) is formed over the entire surface of each substrate 1 and 2.
In the state in which the first and second substrates 1 and 2 are adhesively bonded to each other, the terminals 7c of the first substrate 1 and the terminals 6c of the second substrate, shown in FIGS. 10 and 11, oppose one another. Therefore, if the sealing member 3 used to adhesively bonding the inner surface of the first substrate 1 to the inners surface of the second substrate 2 includes electrically conductive particles, the respective terminals 7c of the first substrate 1 are conducted to the corresponding terminals 6c of the second substrate 2 via the electrically conductive particles contained in the sealing member 3. Thus, if a signal and electric power are supplied to the driving IC 14 via the flexible wiring board 29, the driving IC 14 applies a voltage to a selected stripe-shaped electrode 6a and a selected stripe-shaped electrode 7a thereby controlling the alignment of the liquid crystal of a corresponding pixel (at the intersection of the stripe-shaped electrodes 6a and 7a). As a result, a corresponding image is displayed on the liquid crystal device 10.
FIG. 12 illustrates another example of an electro-optical panel. In this electro-optical panel, an active matrix substrate (first substrate) 82 is formed by disposing pixels in a matrix fashion on the surface of a transparent substrate made of quartz glass or the like wherein each pixel includes a pixel electrode 88 and a thin film transistor (hereinafter referred to as a TFT) serving as a pixel switching device which will be described in detail later. An opposite substrate 83 (second substrate) is disposed opposite the active matrix substrate 82, wherein the opposite substrate 83 is formed by disposing opposite electrodes 112 on the surface of a substrate made of glass having high heat resistance such as Neoceram. An electro-optical material 129 such as a liquid crystal is placed and sealed between the two substrates described above. The active matrix substrate 82 and the opposite substrate 83 are adhesively bonded to each other via a sealing material 200xe2x80x2 containing spacer elements such that they are spaced a determined distance apart from each other. An electro-optical material sealing region 127 is formed in the gap between the two substrates by partitioning the gap with the sealing member 200xe2x80x2, and the electro-optical material 129 is disposed in the electro-optical material sealing region 127. The sealing member 200xe2x80x2 containing spacer elements may be formed of an adhesive component such as an epoxy resin or an acrylic resin in which spacer elements such as glass beads are dispersed. Before adhesively bonding the active matrix substrate 82 and the opposite substrate 83 to each other, spacers 128 in the form of beads or fibers are placed in a dispersive fashion on the active matrix substrate 82 or the opposite substrate 83 so that the gap distance between the active matrix substrate 82 and the opposite substrate 83 bonded to each other is determined by the spacers 128.
In the electro-optical panel 81f described above, a TFT (pixel switching device) is formed in each pixel as shown in FIGS. 13 and 14. In FIGS. 13 and 14, an underlying protective film 201 which is electrically insulating is formed on the surface of a transparent substrate 100 serving as a base element of the active matrix substrate 82, and a silicon film 92 is formed in the shape of an island on the surface of the underlying protective film 201. A gate insulating film 93 is formed on the surface of the silicon film 92, and a scanning line 151 extends across the surface of the gate insulating film 93 so that the scanning line 151 acts as a gate electrode. A region of the silicon film 92, at a location opposing the scanning line 151 via the gate insulating film 93, serves as a channel region 95. A source region 96 is formed at one end of the channel region 95, and a drain region 97 is formed at the other end. A first interlayer insulating film 98 and a second interlayer insulating film 99 are formed on the surface of the TFT 90xe2x80x2 serving as the pixel switching device. A data line 150 is formed on the surface of the first interlayer insulating film 98 wherein the data line 150 is electrically connected to the source region 96 via a contact hole formed in the first interlayer insulating film 98. The pixel electrode 88 is electrically connected to the drain region 97 via contact holes formed in the first and second interlayer insulating films 98 and 99.
Furthermore, an alignment film 94 is formed on the surface of the pixel electrode 88 as shown in FIG. 14. On the opposite substrate 83, opposite electrodes 112 are formed on a transparent substrate 110 serving as a base element of the opposite substrate 83, and an alignment film 113 is formed on the surface of the opposite electrodes 112.
In some cases, although not shown in the figures, a scanning line driving circuit for outputting a scanning signal via the scanning lines 151 and a data line driving circuit for outputting a data signal via the data lines 150 are formed on the active matrix substrate 82. In this case, the scanning line driving circuit and the data line driving circuit may be formed using TFTs having a similar structure to that of the TFT 90xe2x80x2 serving as the pixel switching device.
In the liquid crystal device 10 shown in FIG. 9, if the size of an area where an image is displayed (an image display area in which pixels are disposed in the form of a matrix) is fixed, it is desirable that a peripheral area outside the image display area be small as possible. However, in the conventional liquid crystal device 10, a rather large peripheral area is required to dispose the driving IC 14, and thus the reduction in the area which does not make a direct contribution to displaying an image has a practical limitation.
In the electro-optical panel 81xe2x80x2 shown in FIG. 12, it is desirable that an inexpensive glass substrate be employed as the transparent substrate 100 used in the active matrix substrate 82. It is also preferable to employ a plastic film as the transparent substrate 100. However, in order to employ such a transparent substrate, it is required that TFTs 90xe2x80x2 serving as pixel switching devices and those in the driving circuit be formed at a temperature which is low enough to prevent the substrate from being thermally deformed or degraded. The temperature restriction results in various problems such as low transistor performance of the TFTs which cannot be overcome by the conventional technique of the electro-optical panel 81xe2x80x2.
In view of the above, it is a first object of the present invention to provide an electro-optical device whose peripheral area making no direct contribution to displaying an image is minimized in size by using a novel type of semiconductor device which is not known in the art.
It is a second object of the present invention to provide an electro-optical panel in which each pixel including a pixel electrode and a pixel switching device is formed in a novel structure without encountering a problem caused by heat resistance of a substrate when forming the switching device.
It is a third object of the present invention to provide an electro-optical panel in which the structure of each pixel is improved thereby allowing the gap distance between two substrates, between which an electro-optical material is disposed, to be precisely controlled thereby allowing an improvement in image quality.
According to a first aspect of the present invention, to achieve the above objects, there is provided an electro-optical device including an electro-optical material disposed between first and second electrodes and also including a substrate on which at least either the first or second electrode is formed and on which a plurality of input terminals for inputting a signal from the outside are formed and furthermore on which a semiconductor device for driving said electro-optical material via the first and second electrodes is mounted on an wiring pattern electrically connected to the input terminals, the electro-optical device being characterized in that the semiconductor device includes a plurality of spherical-shaped semiconductor devices each including a semiconductor device element formed on the surface of a spherical-shaped semiconductor material.
The present invention uses a novel type of IC based on the spherical-shaped semiconductor technology developed by Ball Semiconductor, Inc., and disclosed, for example, in xe2x80x9cNikkei Microdevicesxe2x80x9d published Jul. 1, 1998. According to this technology, a spherical semiconductor device is produced by first crystallizing, into a single crystal, a polycrystalline semiconductor material in the form of a spherical particle with a diameter less than 1 mm and then forming a semiconductor device using various semiconductor processes. A feature of the spherical semiconductor device is a high area-to-volume ratio compared to that of a wafer-shaped semiconductor substrate. This feature allows a large surface area to be obtained using a small amount of semiconductor material. This means that an IC having the same capabilities can be realized on a chip with a smaller size. If each semiconductor device is formed in a spherical shape, a plurality of semiconductor devices may be disposed in a dispersive fashion at various available locations. This makes it possible to minimize an area (peripheral area) of the electro-optical device which makes no direct contribution to displaying an image.
In this electro-optical device according to the present invention, the first electrode may be formed on a first substrate and the second electrode may be formed on a second substrate. Furthermore, a liquid crystal may be employed as the electro-optical material.
In the electro-optical device according to the present invention, one or more spherical-shaped semiconductor devices may be mounted in correspondence to each input terminal, without causing large areas to be occupied by the spherical-shaped semiconductor devices because they are small in size.
Alternatively, one or more spherical-shaped semiconductor devices may be mounted in correspondence to a plurality of input terminals. This allows the area which makes no direct contribution to displaying an image to be further reduced.
According to a second aspect of the present invention, there is provided an electro-optical device comprising a first substrate on which pixels are disposed in the form of a matrix, each pixel including a pixel electrode and a pixel switching device for controlling the supply of an image signal to the pixel electrode; a second substrate disposed opposite the first substrate; and an electro-optical material disposed between the first substrate and the second substrate, wherein each pixel switching device is formed on the surface of a spherical-shaped semiconductor material, and spherical-shaped semiconductor devices each including a pixel switching device formed on the surface of a spherical-shaped semiconductor material are disposed in the respective pixels on the first substrate.
In this technique, because pixel switching devices are first produced in the form of spherical-shaped semiconductor devices and then the spherical-shaped semiconductor devices are mounted on the first substrate, the switching devices can be produced using a high-temperature process or the like at an optimum temperature without encountering a limitation in temperature caused by the heat resistance of the substrate. This allows the switching devices to have high transistor performance. Furthermore, because the substrate is not exposed to high temperature when the switching devices are formed, an inexpensive substrate such as a glass substrate or a plastic film may be employed as the substrate. Another advantage is that the spherical-shaped semiconductor has a greater area-to-volume ratio than wafer-shaped semiconductor substrates. Therefore, a large surface area can be obtained using a small amount of semiconductor material, and thus the spherical-shaped semiconductor devices can be disposed in the respective pixels without causing a reduction in the aperture ratio (the ratio of the area which allows light to be passed therethrough and which thus makes a direct contribution to displaying an image to the total area).
In the above-described electro-optical device according to the present invention, the second substrate may include opposite electrodes disposed opposite to the pixel electrodes. Furthermore, a liquid crystal is used as the electro-optical material. In any case, the advantages described above can also be obtained.
Furthermore, in the above-described electro-optical device according to the present invention, the spherical-shaped semiconductor devices may be located between the first substrate and the second substrate so that the spherical-shaped semiconductors serve as spacers which determine the gap distance between the first substrate and the second substrates. If the second substrate is adhesively bonded to the first substrate after mounting the spherical-shaped semiconductor devices on the first substrate, the spherical-shaped semiconductor devices produce a particular gap between the first substrate and the second substrate. Herein, because the spherical-shaped semiconductor devices are placed in the respective pixels at uniform intervals rather than at random intervals, the gap distance between the first substrate and the second substrate is precisely determined. As a result, the thickness of the electro-optical material such as a liquid crystal sealed between the first substrate and the second substrate becomes uniform and thus it becomes possible to control the alignment of the electro-optical material more precisely. Thus, the electro-optical panel according to the present invention can display an image with high quality.
In the present invention, each pixel switching device may be a MIS (metal-insulator-semiconductor) transistor whose gate, source, and drain are connected to a scanning line, a data line, and a pixel electrode, respectively, formed on the first substrate. Furthermore, in the present invention, a scanning line driving circuit for outputting a scanning signal via the scanning line and a data line driving circuit for outputting a data signal via the data line may be formed on the first substrate. In this case, the data line driving circuit and the scanning line driving circuit may be formed of spherical-shaped semiconductor devices including transistors formed on the surface of spherical-shaped semiconductor materials.